John henry



J. H. DALLMEYER hiy gnitrh gram gaunt @ffiriz.

JOHN HENRY .DALLMEY-ER, OF MIDDLESEXGOUNTY, ENGLAND Lowe's Patent No.- 79,323, dated June 30, 1868; patented in England, September 2?, 1866.

his Stlgehnit rtiimt it in tip-s1: goons haunt ant mating tart of tip 5min.

To ALL T0 WHOM '11; MAY CONCERN:

Be it known that I, John HENRY DALLMEYER, of 19 Bl00nlSb111y,-=,street, in thecounty of Middlesex, England, Optician, a subject of the Queen of Great Britain, have invented or discovered certain new and useful Improvements iu Oompound Lenses Suitable for Photographic Uses," and I, the said JOHN HENRY DALLMEYER, do hereby declare the nature of the said invention, and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement thereof; that is to say- My invention relates principally to the production of view-lenses or objectives embracing largo angles. Lenses or objectives constructed according to my invention, differ from all existing double-combination lenses or objectives consisting of two positive combinations, in that the denser or higher refractory medium, 2'. e., the flint-glass lens, occupies-the exterior position in both combinations, that is to say, the convex surface of the flint part of the front combination is exposed to the view or landscape, and that of the back or posterior combination to the screen of the ccmcrzn aud also in that the posterior combination is of smaller diameter than the anterior combination.

And in order that mysaid invention may be most fully understood, I will describe in detail the form I prefer for each of the parts. i

For a lens or objectiv embrccing an angle of about one hundred degrees, and of which the largest, aperture isf the construction is as follows, reference being made tothe annexed diagram, Figure 1.

I form two similar combinations, as A and B, by preferenceof identical foci, or nearly so, and in relation tof (which is the compound or equivalent focus of the entire objective) as two to one. Each combination consists of a deep concavo-convex lens of flint-glass, as a anda, and a deep meniscus of crown-glass, as b and b. The ratio of foci between a nude and a and b, is such, that for the qualities of glass which are being used, each combination, by preference, is achromatic or actinic in itself. The diameter of the front combination, 1%., is, by preference, one-fifth of the compound focus of the objective or f and the radius of curvature of the anterior 5urfuce,r,, of the flint-glass lens a, is, by-preference, also f,. The radius of curvature of the fourth or concave surface 7', ofthe crown-lens b, is to r, as four to three. The internal surfaces, U. r, offlint-lcns a, and r, of croivn lens Z), are, by prefercncmjdcntical and cemented, and such that, for the above focal length and. qualities of glass employed, combination A may be achromatic or nctinio.

The diameter of the bhcl: combination, B, is to that of the front'combinstion, by preference, as one to two, and the radius of curvature of the posterior convex surface 1 of flint-glass lens it, is to the radius of curvature of the anterior convex surface 2', of flint-lens a, by preference, seven to six. The radius of curvature of concave surface 7', of crown-lens b, is to r,,, by preference, as four to three. The radii of curvatures of the internal surfaces, 1'. 0., r, of flint-lens a, and 7- of crown-lens b, are, by preference, identical and cemented, and such that, for the above focal length and qualities of glass employed, combination B may be achromatic or ectinic.

The combinations A and B are separated by an interval, (1'. e., the distance between their internal surfaces) by preference, equal to one-seventh of the compound focal length or" the entire combination or objective, i. 0. f and the diaphragm or stop 0 divides this space in the proportion of the respective diameters of A and B.

The improvements over existing double-combination lenses, free from distortion, and embracing large angles of view, secured by the arrangement of lenses or objectives above detailed, are these:

First. Freedom from a central spot in the resulting picture.

Second. More perfect correction of the central as well as ccccntricnl pencil matic aberrations, hence, for a given largo angle of view, aperture, or, in other words, it is 5, both for spherical and chrothe lens or objective admits of the use of a larger quicker noting than existing lenses constructed for similar purposes.

Third. Greater equality of illuminction throughout the entire surface of the plate covered by the lens. According to the nature of requirements, howeven, other dimensions than those given above can also, with advantage, be employed, as for lenses intended for copying maps and plans only, still retaining the distinctive features of my invention herein set forth.

" Witnesses:

I wouldreniar'kl-that a lens may be constructed 'GCGOI'GIDQ to my invention, of flint-glass only, necesssriiy of two different kinds, as regards density, for the production of'oehromaticity, instead of, as is usual, of crown andfiint-glassL, Then the denser or higher refractive flintglass lens of 'esehof the two combinations occupies the externel oi-exterior position. n I

I I do not claim constructing a. single achromatic combination, with the flint-glass lens at the exterior, but What I iclsim is-e i I v The '(louhle-eombination lens, composed of two positive nehromatic or actinic combinations, each having the higher reflecting denser material atthe exterior. v

Also, the construction of the double-combination lens, with the denser higher retracting material at the exterior and with the posterior achromatic combination ofsmaller diameter than the anterior combinntion.

H. DALLMEYER.

G. F. WARREN, Jonn DEAN,

}Bo'th qf'l%. 17 am eba); Street, London. 

